This is a library for generating form letters, building HTML pages, or filling in templates generally. A `template' is a piece of text that has little Perl programs embedded in it here and there. When you `fill in' a template, you evaluate the little programs and replace them with their values.

You can store a template in a file outside your program. People can modify the template without modifying the program. You can separate the formatting details from the main code, and put the formatting parts of the program into the template. That prevents code bloat and encourages functional separation.

Here's an example of a template, which we'll suppose is stored in the file formletter.tmpl:

Dear {$title} {$lastname},
It has come to our attention that you are delinquent in your
{$monthname[$last_paid_month]} payment. Please remit
${sprintf("%.2f", $amount)} immediately, or your patellae may
be needlessly endangered.
Love,
Mark "Vizopteryx" Dominus

The result of filling in this template is a string, which might look something like this:

Dear Mr. Gates,
It has come to our attention that you are delinquent in your
February payment. Please remit
$392.12 immediately, or your patellae may
be needlessly endangered.
Love,
Mark "Vizopteryx" Dominus

Here is a complete program that transforms the example template into the example result, and prints it out:

When people make a template module like this one, they almost always start by inventing a special syntax for substitutions. For example, they build it so that a string like %%VAR%% is replaced with the value of $VAR. Then they realize the need extra formatting, so they put in some special syntax for formatting. Then they need a loop, so they invent a loop syntax. Pretty soon they have a new little template language.

This approach has two problems: First, their little language is crippled. If you need to do something the author hasn't thought of, you lose. Second: Who wants to learn another language? You already know Perl, so why not use it?

Text::Template templates are programmed in Perl. You embed Perl code in your template, with { at the beginning and } at the end. If you want a variable interpolated, you write it the way you would in Perl. If you need to make a loop, you can use any of the Perl loop constructions. All the Perl built-in functions are available.

The Text::Template module scans the template source. An open brace { begins a program fragment, which continues until the matching close brace }. When the template is filled in, the program fragments are evaluated, and each one is replaced with the resulting value to yield the text that is returned.

A backslash \ in front of a brace (or another backslash that is in front of a brace) escapes its special meaning. The result of filling out this template:

\{ The sum of 1 and 2 is {1+2} \}

is

{ The sum of 1 and 2 is 3 }

If you have an unmatched brace, Text::Template will return a failure code and a warning about where the problem is. Backslashes that do not precede a brace are passed through unchanged. If you have a template like this:

{ "String that ends in a newline.\n" }

The backslash inside the string is passed through to Perl unchanged, so the \n really does turn into a newline. See the note at the end for details about the way backslashes work. Backslash processing is not done when you specify alternative delimiters with the DELIMITERS option. (See "Alternative Delimiters", below.)

Each program fragment should be a sequence of Perl statements, which are evaluated the usual way. The result of the last statement executed will be evaluted in scalar context; the result of this statement is a string, which is interpolated into the template in place of the program fragment itself.

The fragments are evaluated in order, and side effects from earlier fragments will persist into later fragments:

The value of $x set in the first line will persist into the next fragment that begins on the third line, and the values of $diff and $more set in the second fragment will persist and be interpolated into the last line. The output will look something like this:

The Lord High Chamberlain has gotten 42
things for me this year.
That is 25 more than he gave me last year.

There is one special trick you can play in a template. Here is the motivation for it: Suppose you are going to pass an array, @items, into the template, and you want the template to generate a bulleted list with a header, like this:

Here is a list of the things I have got for you since 1907:
* Ivory
* Apes
* Peacocks
* ...

Here we construct the list in a variable called $blist, which we return at the end. This is a little cumbersome. There is a shortcut.

Inside of templates, there is a special variable called $OUT. Anything you append to this variable will appear in the output of the template. Also, if you use $OUT in a program fragment, the normal behavior, of replacing the fragment with its return value, is disabled; instead the fragment is replaced with the value of $OUT. This means that you can write the template above like this:

Here is a list of the things I have got for you since 1907:
{ foreach $i (@items) {
$OUT .= " * $i\n";
}
}

$OUT is reinitialized to the empty string at the start of each program fragment. It is private to Text::Template, so you can't use a variable named $OUT in your template without invoking the special behavior.

All Text::Template functions return undef on failure, and set the variable $Text::Template::ERROR to contain an explanation of what went wrong. For example, if you try to create a template from a file that does not exist, $Text::Template::ERROR will contain something like:

This creates and returns a new template object. new returns undef and sets $Text::Template::ERROR if it can't create the template object. SOURCE says where the template source code will come from. TYPE says what kind of object the source is.

The most common type of source is a file:

new Text::Template ( TYPE => 'FILE', SOURCE => $filename );

This reads the template from the specified file. The filename is opened with the Perl open command, so it can be a pipe or anything else that makes sense with open.

The TYPE can also be STRING, in which case the SOURCE should be a string:

The TYPE can be FILEHANDLE, in which case the source should be an open filehandle (such as you got from the FileHandle or IO::* packages, or a glob, or a reference to a glob). In this case Text::Template will read the text from the filehandle up to end-of-file, and that text is the template:

You may also add a DELIMITERS option. If this option is present, its value should be a reference to an array of two strings. The first string is the string that signals the beginning of each program fragment, and the second string is the string that signals the end of each program fragment. See "Alternative Delimiters", below.

If your program is running in taint mode, you may have problems if your templates are stored in files. Data read from files is considered 'untrustworthy', and taint mode will not allow you to evaluate the Perl code in the file. (It is afraid that a malicious person might have tampered with the file.)

In some environments, however, local files are trustworthy. You can tell Text::Template that a certain file is trustworthy by supplying UNTAINT => 1 in the call to new. This will tell Text::Template to disable taint checks on template code that has come from a file, as long as the filename itself is considered trustworthy. It will also disable taint checks on template code that comes from a filehandle. When used with TYPE => 'string' or TYPE => 'array', it has no effect.

Loads all the template text from the template's source, parses and compiles it. If successful, returns true; otherwise returns false and sets $Text::Template::ERROR. If the template is already compiled, it returns true and does nothing.

You don't usually need to invoke this function, because fill_in (see below) compiles the template if it isn't compiled already.

If there is an argument to this function, it must be a reference to an array containing alternative delimiter strings. See "Alternative Delimiters", below.

Fills in a template. Returns the resulting text if successful. Otherwise, returns undef and sets $Text::Template::ERROR.

The OPTIONS are a hash, or a list of key-value pairs. You can write the key names in any of the six usual styles as above; this means that where this manual says PACKAGE (for example) you can actually use any of

PACKAGE Package package -PACKAGE -Package -package

Pick a style you like and stick with it. The all-lowercase versions may yield spurious warnings about

PACKAGE specifies the name of a package in which the program fragments should be evaluated. The default is to use the package from which fill_in was called. For example, consider this template:

The value of the variable x is {$x}.

If you use $template->fill_in(PACKAGE => 'R') , then the $x in the template is actually replaced with the value of $R::x. If you omit the PACKAGE option, $x will be replaced with the value of the $x variable in the package that actually called fill_in.

You should almost always use PACKAGE. If you don't, and your template makes changes to variables, those changes will be propagated back into the main program. Evaluating the template in a private package helps prevent this. The template can still modify variables in your program if it wants to, but it will have to do so explicitly. See the section at the end on `Security'.

We want to pass in an array which will be assigned to the array @items. Here's how to do that:

@items = ('ivory', 'apes', 'peacocks', );
$template->fill_in();

This is not very safe. The reason this isn't as safe is that if you had a variable named $item_no in scope in your program at the point you called fill_in, its value would be clobbered by the act of filling out the template. The problem is the same as if you had written a subroutine that used those variables in the same way that the template does. ($OUT is special in templates and is always safe.)

One solution to this is to make the $item_no variable private to the template by declaring it with my. If the template does this, you are safe.

But if you use the PACKAGE option, you will probably be safe even if the template does not declare its variables with my:

will fill out the template and use "The King" as the value of $recipient and the list of items as the value of @items. Note that we pass an array reference, but inside the template it appears as an array. In general, anything other than a simple string or number should be passed by reference.

We also want to pass an object, which is in $self; note that we pass a reference to the object, \$self instead. Since we've passed a reference to a scalar, inside the template the object appears as $object.

The full details of how it works are a little involved, so you might want to skip to the next section.

Suppose the key in the hash is key and the value is value.

If the value is undef, then any variables named $key, @key, %key, etc., are undefined.

If the value is a string or a number, then $key is set to that value in the template.

For anything else, you must pass a reference.

If the value is a reference to an array, then @key is set to that array. If the value is a reference to a hash, then %key is set to that hash. Similarly if value is any other kind of reference. This means that

var => "foo"

and

var => \"foo"

have almost exactly the same effect. (The difference is that in the former case, the value is copied, and in the latter case it is aliased.)

In particular, if you want the template to get an object or any kind, you must pass a reference to it:

$template->fill_in(HASH => { database_handle => \$dbh, ... });

If you do this, the template will have a variable $database_handle which is the database handle object. If you leave out the \, the template will have a hash %database_handle, which exposes the internal structure of the database handle object; you don't want that.

Normally, the way this works is by allocating a private package, loading all the variables into the package, and then filling out the template as if you had specified that package. A new package is allocated each time. However, if you also use the PACKAGE option, Text::Template loads the variables into the package you specified, and they stay there after the call returns. Subsequent calls to fill_in that use the same package will pick up the values you loaded in.

If the argument of HASH is a reference to an array instead of a reference to a hash, then the array should contain a list of hashes whose contents are loaded into the template package one after the other. You can use this feature if you want to combine several sets of variables. For example, one set of variables might be the defaults for a fill-in form, and the second set might be the user inputs, which override the defaults when they are present:

If any of the program fragments fails to compile or aborts for any reason, and you have set the BROKEN option to a function reference, Text::Template will invoke the function. This function is called the BROKEN function. The BROKEN function will tell Text::Template what to do next.

If the BROKEN function returns undef, Text::Template will immediately abort processing the template and return the text that it has accumulated so far. If your function does this, it should set a flag that you can examine after fill_in returns so that you can tell whether there was a premature return or not.

If the BROKEN function returns any other value, that value will be interpolated into the template as if that value had been the return value of the program fragment to begin with. For example, if the BROKEN function returns an error string, the error string will be interpolated into the output of the template in place of the program fragment that cased the error.

If you don't specify a BROKEN function, Text::Template supplies a default one that returns something like

Program fragment delivered error ``Illegal division by 0 at
template line 37''

(Note that the format of this message has changed slightly since version 1.31.) The return value of the BROKEN function is interpolated into the template at the place the error occurred, so that this template:

The text has been modified to omit the trailing newline and to include the name of the template file (if there was one). The line number counts from the beginning of the template, not from the beginning of the failed program fragment.

If you supply the BROKEN_ARG option to fill_in, the value of the option is passed to the BROKEN function whenever it is called. The default BROKEN function ignores the BROKEN_ARG, but you can write a custom BROKEN function that uses the BROKEN_ARG to get more information about what went wrong.

The BROKEN function could also use the BROKEN_ARG as a reference to store an error message or some other information that it wants to communicate back to the caller. For example:

If one of the program fragments in the template fails, it will call the BROKEN function, my_broken, and pass it the BROKEN_ARG, which is a reference to $error. my_broken can store an error message into $error this way. Then the function that called fill_in can see if my_broken has left an error message for it to find, and proceed accordingly.

If you give fill_in a SAFE option, its value should be a safe compartment object from the Safe package. All evaluation of program fragments will be performed in this compartment. See Safe for full details about such compartments and how to restrict the operations that can be performed in them.

If you use the PACKAGE option with SAFE, the package you specify will be placed into the safe compartment and evaluation will take place in that package as usual.

If not, SAFE operation is a little different from the default. Usually, if you don't specify a package, evaluation of program fragments occurs in the package from which the template was invoked. But in SAFE mode the evaluation occurs inside the safe compartment and cannot affect the calling package. Normally, if you use HASH without PACKAGE, the hash variables are imported into a private, one-use-only package. But if you use HASH and SAFE together without PACKAGE, the hash variables will just be loaded into the root namespace of the Safe compartment.

If your template is going to generate a lot of text that you are just going to print out again anyway, you can save memory by having Text::Template print out the text as it is generated instead of making it into a big string and returning the string. If you supply the OUTPUT option to fill_in, the value should be a filehandle. The generated text will be printed to this filehandle as it is constructed. For example:

$template->fill_in(OUTPUT => \*STDOUT, ...);

fills in the $template as usual, but the results are immediately printed to STDOUT. This may result in the output appearing more quickly than it would have otherwise.

If you use OUTPUT, the return value from fill_in is still true on success and false on failure, but the complete text is not returned to the caller.

If this option is present, its value should be a reference to a list of two strings. The first string is the string that signals the beginning of each program fragment, and the second string is the string that signals the end of each program fragment. See "Alternative Delimiters", below.

If you specify DELIMITERS in the call to fill_in, they override any delimiters you set when you created the template object with new.

The basic way to fill in a template is to create a template object and then call fill_in on it. This is useful if you want to fill in the same template more than once.

In some programs, this can be cumbersome. fill_this_in accepts a string, which contains the template, and a list of options, which are passed to fill_in as above. It constructs the template object for you, fills it in as specified, and returns the results. It returns undef and sets $Text::Template::ERROR if it couldn't generate any results.

Notice how we included the template in-line in the program by using a `here document' with the << notation.

fill_this_in is a deprecated feature. It is only here for backwards compatibility, and may be removed in some far-future version in Text::Template. You should use fill_in_string instead. It is described in the next section.

It is stupid that fill_this_in is a class method. It should have been just an imported function, so that you could omit the Text::Template-> in the example above. But I made the mistake four years ago and it is too late to change it.

fill_in_string is exactly like fill_this_in except that it is not a method and you can omit the Text::Template-> and just say

print fill_in_string(<<'EOM', ...);
Dear {$name},
...
EOM

To use fill_in_string, you need to say

use Text::Template 'fill_in_string';

at the top of your program. You should probably use fill_in_string instead of fill_this_in.

The ... are passed to fill_in as above. The filename is the name of the file that contains the template you want to fill in. It returns the result text. or undef, as usual.

If you are going to fill in the same file more than once in the same program you should use the longer new / fill_in sequence instead. It will be a lot faster because it only has to read and parse the file once.

The text The King doesn't get into the form letter. Why not? Because $recipient is a my variable, and the whole point of my variables is that they're private and inaccessible except in the scope in which they're declared. The template is not part of that scope, so the template can't see $recipient.

If that's not the behavior you want, don't use my. my means a private variable, and in this case you don't want the variable to be private. Put the variables into package variables in some other package, and use the PACKAGE option to fill_in:

All variables are evaluated in the package you specify with the PACKAGE option of fill_in. if you use this option, and if your templates don't do anything egregiously stupid, you won't have to worry that evaluation of the little programs will creep out into the rest of your program and wreck something.

Nevertheless, there's really no way (except with Safe) to protect against a template that says

so don't go filling in templates unless you're sure you know what's in them. If you're worried, or you can't trust the person who wrote the template, use the SAFE option.

A final warning: program fragments run a small risk of accidentally clobbering local variables in the fill_in function itself. These variables all have names that begin with $fi_, so if you stay away from those names you'll be safe. (Of course, if you're a real wizard you can tamper with them deliberately for exciting effects; this is actually how $OUT works.) I can fix this, but it will make the package slower to do it, so I would prefer not to. If you are worried about this, send me mail and I will show you what to do about it.

Lorenzo Valdettaro pointed out that if you are using Text::Template to generate TeX output, the choice of braces as the program fragment delimiters makes you suffer suffer suffer. Starting in version 1.20, you can change the choice of delimiters to something other than curly braces.

In either the new() call or the fill_in() call, you can specify an alternative set of delimiters with the DELIMITERS option. For example, if you would like code fragments to be delimited by [@-- and --@] instead of { and }, use

... DELIMITERS => [ '[@--', '--@]' ], ...

Note that these delimiters are literal strings, not regexes. (I tried for regexes, but it complicates the lexical analysis too much.) Note also that DELIMITERS disables the special meaning of the backslash, so if you want to include the delimiters in the literal text of your template file, you are out of luck---it is up to you to choose delimiters that do not conflict with what you are doing. The delimiter strings may still appear inside of program fragments as long as they nest properly. This means that if for some reason you absolutely must have a program fragment that mentions one of the delimiters, like this:

It may be safer to choose delimiters that begin with a newline character.

Because the parsing of templates is simplified by the absence of backslash escapes, using alternative DELIMITERS may speed up the parsing process by 20-25%. This shows that my original choice of { and } was very bad.

Suppose you would like to use strict in your templates to detect undeclared variables and the like. But each code fragment is a separate lexical scope, so you have to turn on strict at the top of each and every code fragment:

Because we didn't put use strict at the top of the second fragment, it was only active in the first fragment, and we didn't get any strict checking in the second fragment. Then we mispelled $foo and the error wasn't caught.

Text::Template version 1.22 and higher has a new feature to make this easier. You can specify that any text at all be automatically added to the beginning of each program fragment.

When you make a call to fill_in, you can specify a

PREPEND => 'some perl statements here'

option; the statements will be prepended to each program fragment for that one call only. Suppose that the fill_in call included a

The code in the second fragment would fail, because $boo has not been declared. use strict was implied, even though you did not write it explicitly, because the PREPEND option added it for you automatically.

There are two other ways to do this. At the time you create the template object with new, you can also supply a PREPEND option, in which case the statements will be prepended each time you fill in that template. If the fill_in call has its own PREPEND option, this overrides the one specified at the time you created the template. Finally, you can make the class method call

Text::Template->always_prepend('perl statements');

If you do this, then call calls to fill_in for any template will attach the perl statements to the beginning of each program fragment, except where overridden by PREPEND options to new or fill_in.

This section is technical, and you should skip it on the first few readings.

Normally there are three places that prepended text could come from. It could come from the PREPEND option in the fill_in call, from the PREPEND option in the new call that created the template object, or from the argument of the always_prepend call. Text::Template looks for these three things in order and takes the first one that it finds.

In a subclass of Text::Template, this last possibility is ambiguous. Suppose S is a subclass of Text::Template. Should

Text::Template->always_prepend(...);

affect objects in class Derived? The answer is that you can have it either way.

The always_prepend value for Text::Template is normally stored in a hash variable named %GLOBAL_PREPEND under the key Text::Template. When Text::Template looks to see what text to prepend, it first looks in the template object itself, and if not, it looks in $GLOBAL_PREPEND{class} where class is the class to which the template object belongs. If it doesn't find any value, it looks in $GLOBAL_PREPEND{'Text::Template'}. This means that objects in class Derivedwill be affected by

Text::Template->always_prepend(...);

unless there is also a call to

Derived->always_prepend(...);

So when you're designing your derived class, you can arrange to have your objects ignore Text::Template::always_prepend calls by simply putting Derived->always_prepend('') at the top of your module.

Of course, there is also a final escape hatch: Templates support a prepend_text that is used to look up the appropriate text to be prepended at fill_in time. Your derived class can override this method to get an arbitrary effect.

> Most of my pages contain JavaScript and Stylesheets.
> How do I change the template identifier?

Jennifer is worried about the braces in the JavaScript being taken as the delimiters of the Perl program fragments. Of course, disaster will ensue when perl tries to evaluate these as if they were Perl programs. The best choice is to find some unambiguous delimiter strings that you can use in your template instead of curly braces, and then use the DELIMITERS option. However, if you can't do this for some reason, there are two easy workarounds:

1. You can put \ in front of {, }, or \ to remove its special meaning. So, for example, instead of

if (br== "n3") {
// etc.
}

you can put

if (br== "n3") \{
// etc.
\}

and it'll come out of the template engine the way you want.

But here is another method that is probably better. To see how it works, first consider what happens if you put this into a template:

{ 'foo' }

Since it's in braces, it gets evaluated, and obviously, this is going to turn into

foo

So now here's the trick: In Perl, q{...} is the same as '...'. So if we wrote

People sometimes try to put an initialization section at the top of their templates, like this:

{ ...
$var = 17;
}

Then they complain because there is a 17 at the top of the output that they didn't want to have there.

Remember that a program fragment is replaced with its own return value, and that in Perl the return value of a code block is the value of the last expression that was evaluated, which in this case is 17. If it didn't do that, you wouldn't be able to write {$recipient} and have the recipient filled in.

To prevent the 17 from appearing in the output is very simple:

{ ...
$var = 17;
'';
}

Now the last expression evaluated yields the empty string, which is invisible. If you don't like the way this looks, use

{ ...
$var = 17;
($SILENTLY);
}

instead. Presumably, $SILENTLY has no value, so nothing will be interpolated. This is what is known as a `trick'.

Every effort has been made to make this module compatible with older versions. The only known exceptions follow:

The output format of the default BROKEN subroutine has changed twice, most recently between versions 1.31 and 1.40.

Starting in version 1.10, the $OUT variable is arrogated for a special meaning. If you had templates before version 1.10 that happened to use a variable named $OUT, you will have to change them to use some other variable or all sorts of strangeness will result.

Between versions 0.1b and 1.00 the behavior of the \ metacharacter changed. In 0.1b, \\ was special everywhere, and the template processor always replaced it with a single backslash before passing the code to Perl for evaluation. The rule now is more complicated but probably more convenient. See the section on backslash processing, below, for a full discussion.

In Text::Template beta versions, the backslash was special whenever it appeared before a brace or another backslash. That meant that while {"\n"} did indeed generate a newline, {"\\"} did not generate a backslash, because the code passed to Perl for evaluation was "\" which is a syntax error. If you wanted a backslash, you would have had to write {"\\\\"}.

In Text::Template versions 1.00 through 1.10, there was a bug: Backslash was special everywhere. In these versions, {"\n"} generated the letter n.

The bug has been corrected in version 1.11, but I did not go back to exactly the old rule, because I did not like the idea of having to write {"\\\\"} to get one backslash. The rule is now more complicated to remember, but probably easier to use. The rule is now: Backslashes are always passed to Perl unchanged unless they occur as part of a sequence like \\\\\\{ or \\\\\\}. In these contexts, they are special; \\ is replaced with \, and \{ and \} signal a literal brace.

Examples:

\{ foo \}

is not evaluated, because the \ before the braces signals that they should be taken literally. The result in the output looks like this:

{ foo }

This is a syntax error:

{ "foo}" }

because Text::Template thinks that the code ends at the first }, and then gets upset when it sees the second one. To make this work correctly, use

{ "foo\}" }

This passes "foo}" to Perl for evaluation. Note there's no \ in the evaluated code. If you really want a \ in the evaluated code, use

{ "foo\\\}" }

This passes "foo\}" to Perl for evaluation.

Starting with Text::Template version 1.20, backslash processing is disabled if you use the DELIMITERS option to specify alternative delimiter strings.

In the past some people have fretted about `violating the package boundary' by examining a variable inside the Text::Template package. Don't feel this way. $Text::Template::ERROR is part of the published, official interface to this package. It is perfectly OK to inspect this variable. The interface is not going to change.

If it really, really bothers you, you can import a function called TTerror that returns the current value of the $ERROR variable. So you can say:

The CGI module provides functions for `sticky widgets', which are form input controls that retain their values from one page to the next. Sometimes people want to know how to include these widgets into their template output.

It's totally straightforward. Just call the CGI functions from inside the template:

This software is version 1.45. It may have bugs. Suggestions and bug reports are always welcome. Send them to mjd-perl-template+@plover.com. (That is my address, not the address of the mailing list. The mailing list address is a secret.)

Text::Template version 1.45
Copyright (C) 2008 Mark Jason Dominus
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version. You may also can
redistribute it and/or modify it under the terms of the Perl
Artistic License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received copies of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

for demanding less verbose fragments like they have in ASP, for helping me figure out the Right Thing, and, especially, for talking me out of adding any new syntax. These discussions resulted in the $OUT feature.